Pub. date: 2008 | Online Pub. Date: April 25, 2008 | DOI: 10.4135/9781412963893 | Print ISBN: 9781412958783 | Online ISBN: 9781412963893| Publisher:SAGE Publications, Inc.About this encyclopedia
North Atlantic Oscillation
Elena Voskresenskaya & Alexander Boris Polonsky
THE NORTH ATLANTIC Oscillation (NAO) is quasi-periodic shifts in the relative strength of the quasi-permanent centers of high atmospheric pressure over the Azores and low atmospheric pressure between Greenland and Iceland (the Azores High and Iceland Low). It is a major large-scale mode of the atmospheric circulation over the extratropical ocean in the Northern Hemisphere. The NAO intensity is at a maximum in winter. It governs the large-scale variability of hydrometeorological fields over the North Atlantic, North America, and northern Europe, as became clear after a pioneer paper published by Sir Walker and co-author in 1932. Recently, the NAO has been set in a broader spatial context of hemispheric climatic variations, both at the surface and aloft as follows, for instance, from generalized publications of John Marshal, et al, and Alexander Polonsky, et al. As a measure of NAO, a special index is often used. This index is the normalized ...